This invention relates to control apparatus and methods in general, and to heat transfer systems including air conditioning systems and to apparatus and methods for controlling such systems and for sensing and indicating low fluid charge conditions therein.
Automatically controlled systems in homes, automobiles, and industry are in widespread use. Such systems include air conditioners, heat pumps, furnaces, servomechanical, robotic, and other systems. All such systems sense and/or control at least one physical variable such as pressure, temperature, displacement, velocity and force, among others. There is a continuing and increasing need for sensing and control devices which accurately monitor a physical variable on a continuous basis, which effect one or more desired control functions at any one or more preselected levels of the physical variable, and which monitor themselves for abnormal conditions which may adversely affect operation.
Without limiting the intended scope of application of the invention disclosed herein, the background of the invention is discussed in connection with the specific field of refrigerant pressure control apparatus for air conditioning systems. One of the control devices in wide use for this purpose is a pressure activated switch as shown in U.S. Pat. No. 4,351,105 is responsive to the refrigerant pressure in the suction line of an automotive air conditioner increasing to a predetermined value whereupon a snap-action member would move from one configuration to another one to actuate switch contacts, and when the refrigerant pressure decreases to a second lower predetermined value the snap-action member would return to its original configuration and move the switch contacts back to their original mode thereby to control the energization of the compressor. This is an effective pressure sensing and control device for the particular predetermined pressure to which one calibrates or adjusts the device and for its particular pressure differential. As more sophisticated control systems are developed a need has arisen for control apparatus, methods for controlling such apparatus, and heat transfer systems which can be programmed to respond to any one or more of a number of different preselected pressures to provide various desired control functions, increase efficiency and detect abnormal conditions in the systems.
It is believed that heretofore detection of abnormally low refrigerant charge on the one hand, and pressure sensing and controlling of the air conditioner on the other, have been accomplished, if at all, by separate mechanisms. It is also believed that heretofore pressure switches were not known which could be made to accurately respond to each selected one of a number of different preselected pressures and avoid premature changes of state between off and on in an air conditioner or other system. In addition, it is believed that prior control apparatus has been unable to be made sufficiently reliable, uncomplicated, compact and economical to fulfill present-day needs for greater efficiency, convenience of use and sophisticated features in air conditioning and other systems.